In spite of a large part of the world being covered with water, we do not get sufficient fresh water. With the increased rate of industrialization, even the available fresh water sources are getting polluted day by day making it unusable without proper treatment. The level of ground water is also gradually going down due to higher withdrawal of water from ground and scanty rainfall.
In coastal regions, the availability of fresh water is even scarcer as the ground water is also saline. Fresh water resources are under pressure in many cities and this will increase the demand for recycled water. Development and industrialization cannot sacrifice due to lack of water availability. Some alternatives need to be found which involve reducing use of water in industry, conservation at different levels and most importantly with the reuse of wastewater after its proper treatment. This is where wastewater recycling comes in.
Three types of processes are commonly used for treatment and recycle of effluents. These are physic-chemical, biological and membrane /ion-exchange processes.
Physic-chemical processes are used to remove suspended and colloidal impurities. These processes offer a good pre-treatment to downstream biological and membrane processes. Biological processes are used to remove dissolved organics from effluent and thus to reduce chemical and bio-chemical oxygen demands (COD/BOD) of the effluent. Biologically treated effluent containing dissolved salts and residual impurities are removed in processes such as membrane technology base reverse osmosis, electro-dialysis or ion exchange technique.